1. Field of the Invention
The present invention generally relates generally to a wireless communication technology suitable for establishing a communication link between wireless devices, and more particularly, to a method and apparatus for wireless communication using an acoustic signal.
2. Description of the Related Art
Wireless auxiliary devices, such as telephone headset assemblies, earphones, etc., communicate with their respective base devices (e.g., a telephone, a communication terminal, a mobile PC, a player, etc.) via a radio channel in a digital transmission scheme designed for transmission of voice and music programs.
The use of a radio channel for transmission in a digital format leads to a larger effective range (10 ms or greater) and ensures transmission confidentiality when using a specific encryption technique. For wireless earphones and telephone headset assemblies, standardized systems of digital radio communication, such as Bluetooth or Wireless-Fidelity (Wi-Fi), are commonly used through a wireless link. Despite their advantages, the devices using this transmission technique still have some substantial drawbacks.
For example, for an initial establishment of a secure link between two devices, i.e., a link that is protected against unauthorized access and eavesdropping, the two devices need to identify each other and exchange cryptographic keys. Unfortunately, because the radio channel radiates a decent distance from the paired devices and can be easily monitored by a malicious party, it is not suitable for such a type of data transmission.
In the existing models of Bluetooth wireless telephone headsets, a Personal Identification Number (PIN) code-based method is used to connect devices. More specifically, a PIN code (i.e., a combination of digits and symbols) is stored in a memory of the auxiliary device and at the same time, it is printed in paper or written in an electronic format document for a given device.
A method for establishing a wireless communication link between the auxiliary device and the base device is schematically illustrated in FIG. 1 and performed in the following procedure.
(1) Wireless transceivers of the both devices are turned on and the base device searches for available auxiliary devices, e.g., Bluetooth type devices, such as a hands-free headset.
(2) The base device identifies its “own” auxiliary device by name in a list of the auxiliary devices detected by the base device.
(3) The PIN code of the auxiliary device is then input to the base device through a keyboard.
(4) Subsequently, the connected devices carry out an authentication procedure by applying a shared, private PIN code and exchange encrypted data through a radio channel (e.g., various authentication and encryption algorithms may be available).
(5) If both the devices use the same PIN code, the authentication and encryption procedures are successful and a communication channel is established (i.e., data exchange between the devices is permitted). Otherwise, the communication channel setup is not established.
In the above-described procedure, a user performs operations (1)-(3). However, the shared, private PIN code cannot be transmitted through the radio channel because a radio signal from the device (e.g., a Bluetooth signal) may be intercepted by a malicious party, even over a considerable distance. For example, even though class-2 apparatuses have a nominal effective range of only 10 m, tests have shown that with a high-quality receiver and a class-2 beamed antenna, the signal may be received error-free at a distance of up to 1.8 km.
Accordingly, the user should personally enter the PIN code and should ensure confidentiality of this information.
Unfortunately, the foregoing approach also has a number of drawbacks in terms of security and usability.
First, the PIN code information must always be available to the user when pairing devices, which is not always possible, because the PIN code documentation may be lost or unavailable at the moment.
Secondly, the PIN code should be long enough for reliable protection of the devices against unauthorized access. However, the keyboard is usually emulated on a display in the devices, which may be inconvenient for entering the long PIN code. Consequently, the probability of error occurrence is increased during the manual entry of a long PIN code, and it more likely that a long PIN code will be forgotten by the user.
To overcome these drawbacks, manufacturers of telephone headsets and other similar auxiliary devices have simplified the pairing procedure, using a shorter and/or easier PIN code to remember, for example, “0000”. However, these shorter PIN codes are more susceptible to potential attacks from a malicious party (e.g., parallel connection of other devices to the base device and its monitoring).
Moreover, even if the manufacturers use a longer PIN code, the system may still be in danger of unauthorized access, if the PIN code is fixed. For example, if an intruder somehow manages to find out the PIN code (e.g., to oversee the documentation, to peep entry on the display, etc.), then in the future the intruder will be able to use this information any time to establish an unauthorized connection with the device (e.g., the intruder can use an automobile hands-free kit as an eavesdropping device).
A more secure and simple method for establishing a wireless communication link is known (i.e., a new specification of Bluetooth version 2.1,). By using this newer encryption method with a public key, the standard developers have managed to achieve enhanced protection of communication with a comparatively short PIN code (i.e., a 6-digit PIN code provides the same protection degree as a 15-unit alphanumeric PIN code defined in the previous standards). However, still, the user must enter the PIN code manually using a keyboard, and when an auxiliary device has no display area and/or data entering device, which is quite common in telephone headset assemblies and earphones, then the PIN code is fixed.
Another drawback with the above-described methods is that prior to beginning the connection, the auxiliary device must be in a “visible” or “detectable” mode for performing operations (1) and (2), i.e., the auxiliary device must respond to requests of another device that attempts to establish a link, which is also potentially dangerous (e.g., a malicious party might, in such a manner, detect a device that is left in a car and then break into the car to steal it).
Another method of the wireless communication link establishment and the wireless communication system uses a key that is transmitted through an additional radio channel. In this case, an additional Near Field Communication (NFC) transceiver and controller should be introduced to the auxiliary device, thus considerably complicating the structure, increasing the mass/volume and cost of the device, and weakening its competitiveness in the market.
Another technique for establishing a wireless communication link and a wireless communication system is disclosed in Russian Patent Application No. RU2005130483, H04L 12/56, SONY ERICKSON MOBILE COMMUNICATIONS AB (SE), which was published Jan. 27, 2006. In this reference, the communication link establishment procedure is initiated between a base device and an auxiliary device in the auxiliary device. Then a communication signal is generated in the auxiliary device and converted to a signal for transmission through an additional communication link based on a mobile cellular network, and transmitted to the turned-on base device by cellular communication. An operation mode is set according to a basic communication link of the auxiliary device. The communication signal is extracted from the received data in the base device. If the received communication signal is identical to a communication signal stored in the base device, a communication link is established between the auxiliary device and the base device in accordance with the basic communication link.
However, in the reference above, both devices are required to connect to the cellular network, although many devices (e.g., an MP3 player, a wireless headset, etc.) do not provide cellular connectivity. Moreover, network operator services are paid services (e.g., Short Message Service (SMS)), which is not economically advantageous for the user. Further, the cellular network may not always be available at all times and locations. Finally, during a heavy network load, the link establishment may take a long time.